Economists say a third factor, one with profound political implications, is tax morale. This is a catchall term for various forces that motivate people to pay taxes, including social norms, democratic values, civic pride, transparent government spending, and trust in leadership and fellow citizens. People are more inclined to fudge (yes, economists use that word) their tax forms if they think others aren’t paying their fair share.

None of this would seem to bode especially well for tax morale in the U.S., where faith in government has been dropping for decades. So why are Americans still paying? One possibility is that declining trust has been offset by reforms that made cheating harder. Since 1987, to take one example, tax filers have been required to list Social Security numbers for dependents, a change that generated almost $3 billion in revenue, as the number of dependents nationwide shrank by millions. (Suspiciously, some of the disappeared had names like Fluffy.)

A more worrisome possibility is that tax morale has lagged behind declining trust, and will yet fall. High-profile tax-avoidance schemes—like those detailed in the so-called Panama Papers, or by The New York Times’s reporting on the Trump family’s tax dodges—could help erode morale.